Modular Chiral Bisoxalamide-Copper-Catalyzed Asymmetric Oxo-Diels-Alder Reaction: Carbonyl Coordination for High Enantio- and Diastereocontrols

摘要

The chiral bis-oxalamides (CBOA), readily derived from optically pure 1,2-diphenylethylenediamine (DPEN), were proven to be a class of efficient C-2-symmetric chiral ligands for copper(II)-catalyzed asymmetric inverse-electron demand oxo-Diels-Alder reactions between beta,gamma-unsaturated alpha-ketoesters and 2,3-dihydrofuran or 3,4-dihydro-2H-pyran. The reactions proceeded smoothly under mild conditions to afford the corresponding [4 + 2] cycloadducts in high yields with good enantioselectivities (up to 94% ee) and diastereoselectivities (up to 99:1 dr). DFT calculations demonstrated that carbonyl coordination of the chiral ligand to Cu(II) was crucial for the high stereoinduction. These CBOA ligands exhibited high catalytic efficiency in this reaction, which combined with some other salient features of structural fine tunability, chemical stability, and ready accessibility might endow more practical applications in asymmetric catalytic reactions.